The invention relates to a device for driving boreholes in the ground, as is disclosed in DE 43 32113 A 1.
Horizontal boreholes, in particular having a borehole diameter of approximately 150 mm to 1 300 mm, and also vertical boreholes are produced in the ground using drilling devices in which a rotation ally driven shaft is mounted rotatably inside a machine housing. A drill head is arranged on the end of the shaft facing the rock face or the borehole bottom.
The drill head can be of various designs depending on the nature of the soil in which the borehole is to be sunk. Difficulties thus frequently arise when the nature of the soil to be removed varies over the length of the drill, For instance, rock drill heads generally equipped with rollers, bits or disks become stuck in soft, for example loamy, soils; by contrast, drill heads displaying good drilling performances in loamy or loose soils rapidly fail “due to high wear on encountering rock or large stones.
In the device disclosed in DE 43 32113 A1, this problem is to be solved by the drill head being caused to make a wobbling movement, with the result that it executes rapid percussive movements with high frequency and, accordingly, with high kinetic energy against the rock face or borehole bottom, yet simultaneously clears the detached drilled material with a high degree of torque and at a low speed, or, if the soil at the rock face is too soft for spalling, peels off soil with a high degree of torque. The percussive effect is particularly intended to significantly increase drill lead-through (drilling progress) where relatively hard formations are encountered.
To produce the wobbling movement, the shaft journal, directed toward the rock face, of the driven main shaft of the device, on which journal the drill head is rotatably mounted, is placed at an acute angle in relation to the axis of the main shaft. If the main shaft is then driven in rotation, the drill head wobbles at a frequency corresponding to the rotational frequency of the main shaft. The amplitude of the wobbling movement is dependent on the distance of the wobble center point and the size of the wobble angle.
To produce the slow intrinsic rotational speed of the drill head, the drill head is provided with an external bevel wheel which runs in a stationary internal bevel wheel during the wobbling movement. As a result, the drill head is set at a rotational speed directed oppositely to the main shaft, specifically with a gear reduction which depends on the configuration of the external bevel wheel relative to that of the internal bevel wheel. Gear reductions of 30:1 to 60:1 should be achievable.
Although the device disclosed in DE 43 32 113 A 1 has been shown to be suitable for loosening soil having a high degree of variation, a disadvantage is that the rotational speed of the drill head is not optimal for many soil conditions, since it is usually too high.
A further disadvantage is that the drill head subjected to a significant degree of wear due to the drilling process is expensive and complicated to manufacture on account of the external bevel wheel, resulting in an increase in the running operating costs of this device.
An additional disadvantage is the fact that the bevel wheels running on one another are subjected to an increased degree of wear as a result of penetrating waste.
A final disadvantage is the fact that large pieces of drilled material in particular are not transported away reliably and the conveying line tends to clog up.